Ash dieback disease

Ash dieback is spreading throughout Hampshire and we will see the loss of most of our ash trees. This will have a significant impact on our landscape and wildlife. More importantly, dead and dying ash trees pose a risk to life and property and this risk must be addressed.

What is ash dieback

Ash dieback is a devastating disease which is spreading across Hampshire. It is predicted to severely affect or kill over 90% of ash trees and was confirmed in Hampshire in 2014. This disease will impact wooded landscapes across Hampshire and the UK. Ash dieback was confirmed in Hampshire in 2014 and is spreading. Ash is a very common tree in Hampshire in woodlands and hedgerows and is important for wildlife and for wood products.

The disease, also known as Chalara is caused by a fungus, (Hymenoscyphus fraxineus). This affects the vascular system of ash trees, inhibiting the tree’s ability to draw nutrients up into its upper branches. The disease causes leaf loss and crown dieback in affected trees and will in most cases lead to tree death particularly in younger trees. Evidence from continental Europe suggests that older, mature ash trees can survive infection for longer and continue to provide landscape and wildlife benefits for some time. However, over a period of 20 years we can expect a mortality rate of around 85% of all ash trees. 

Ash trees are the third most common tree in Britain after oak and birch - there are 80 million ash trees in the UK.

How widespread is ash dieback in Hampshire

Ash dieback on Hampshire County Council’s farmed and countryside estate

Hampshire Countryside Service manages over 3,000 hectares of countryside, the majority of which contains ash trees. The Countryside Service has been monitoring the spread of ash dieback over the last few years on a site-by-site basis. The surveys show ash dieback is widespread with ‘hot spots’ where action is being undertaken. We are working with partners to formulate appropriate plans and actions to respond to the spread of ash dieback.

Ash dieback on Hampshire‘s highways

Hampshire Highways has been carrying out detailed surveys of ash trees along the highway network since 2018. On average there is a ‘significant ash tree’ (an ash tree with a trunk diameter of more than 20 centimetres) within falling distance of the carriageway every 326 metres of Hampshire’s primary highway routes. Less than 5% of these surveyed trees have displayed severe signs of ash dieback and, where this has been the case, these trees have been removed as swiftly as possible. The number of diseased ash trees that need to be removed alongside the highway is expected increase as ash dieback continues to spread.

Hampshire Highways will continue to closely monitor ash dieback alongside the highway in accordance with established highway policy. Hampshire Highways is also committed to replacing any highway tree that is removed for highway safety and will support appropriate replanting where there is sufficient space above and below ground.

What does ash dieback look like

The main signs of ash dieback are:

  • Dead branches
  • Blackening of leaves, which often hang limply on the tree
  • Discoloured stems, often with a diamond-shaped lesion where a leaf was attached
  • Trees may eventually drop limbs, collapse or fall

The symptoms are often easier to spot in mid to late summer, when a healthy ash tree should be in full leaf. Ash dieback is much harder to identify in autumn when leaves are naturally changing colour and falling

Once a tree is infected the disease is usually fatal - but some trees are tolerant or resistant to infection. 

Mature ash trees infected by ash dieback may survive for several years but often succumb to a secondary attack by other pests or diseases. To help you spot symptoms of the disease please visit the Forestry Commission's guide.

How is ash dieback spread

Ash dieback can spread locally (over tens of miles) by wind dispersal. The reproductive stage of the fungus grows on the previous year's fallen leaves. It produces fruiting bodies that release spores between June and September. These spores are dispersed by the wind and settle on the leaves of healthy trees. If a healthy tree receives a high enough dose of spores, it too will become infected. Over longer distances, the disease may be spread by the movement of infected ash plants.

Advice for woodland managers and countryside workers

A manual for ‘Managing ash in woodlands in light of ash dieback’ has been published by The Forestry Commission for woodland managers and is linked at the bottom of this page. It includes biosecurity measures to help prevent spreading diseases. A Plant Health Order introduced in 2012 prohibits all imports of ash seeds, plants and trees, as well as all internal movement of ash seeds, plants and trees

Advice for countryside visitors and householders

The risk of spreading ash dieback disease by visiting a forested area is low. But you can help by following the advice from the Forestry Commission for the public, on minimising spread. Householders with ash trees suspected of being infected should dispose of leaves by composting in situ or in their normal general rubbish bin. They must not be put in your green waste bin for composting

What are the impacts and what can be done

Ash dieback is likely to cause significant damage to the UK's ash tree population. Experience from Europe has shown that young trees are often killed quite quickly. Older, mature trees may survive for longer and they are often brought down by secondary infections, such as honey fungus.

There is no cure for ash dieback, but some trees are less susceptible to the disease. Investigating this natural resistance could be the best way to secure the future of the UK's ash trees.

There is agreement from scientists that ash dieback cannot be controlled in any permanent way. Scientific evidence suggests that the best way to fight this disease is to allow it to spread through the ash population and wait for trees with natural resistance to regenerate woodlands.

Current situation in the UK

The Forestry Commission has completed a survey of ash dieback confirmed findings across the UK. As of September 2018, 49.2% of the UK landmass, split by 10km grid squares, was found to have been infected.

You can also report suspected ash dieback symptoms using a smartphone by visiting the Tree A!ert website and completing the online form.

Our ash dieback action plan 

Hampshire County Council is currently producing an action plan to help mitigate the impact of ash dieback on the county’s nature reserves. The first stage of this will be to identify any affected ash trees where there could be a risk of branches or entire trees falling. These trees will be felled where they would pose a significant and unavoidable threat to public safety

The wider impact of ash dieback on wildlife will be addressed through a combination of replanting appropriate trees and allowing natural regeneration to take place

What to do about diseased ash trees in gardens or on your land

It is vital that people who are concerned about the trees in their garden or woodland do not attempt to remove any ash trees without first seeking expert advice. It is important that you:

  • Do not proactively remove healthy ash trees due to ash dieback concerns. Ash trees are a vital habitat for birds and insects and some ash trees may have a natural resistance. Seeds from surviving ash trees can also be used for replanting schemes
  • If you think a tree might be infected by ash dieback, watch the videos available on the Observatree website about ash die back symptoms, or consult the ash dieback symptom guides on the Forest Research website. Double check that the tree is an ash tree and not a rowan tree (also known as a mountain ash). Rowan trees are easily mistaken for ash and are not susceptible to ash dieback
  • If you think a tree is infected with ash dieback, report it to the Forestry Commission online using their Tree A!ert website
  • You are not required to take any particular action if you own infected ash trees, unless the Forestry Commission asks you to
  • Diseased mature ash trees do not need to be removed unless they pose a significant safety risk, as they are valuable to wildlife, take longer to die and can help us learn more about genetic strains that might be resistant to the disease
  • Keep an eye on the trees' safety as the disease progresses, and prune or fell them if they or their branches threaten to cause injury or damage
  • In garden situations, you can help to slow the spread of the disease by collecting and burning the ash tree’s fallen leaves (if permitted in your area), or burying or composting its fallen leaves - this breaks the fungus's life cycle

Most trees adjacent to the public highway and within falling distance of roads and footpaths will be the responsibility of private landowners. All landowners and managers have a legal duty to maintain their trees and should ensure that any trees on their land are inspected appropriately and that action is taken to remove tree hazards. With Ash dieback now widespread, it’s particularly important that a landowner’s ash trees are inspected, and that action is taken to remove these where they constitute a hazard, especially alongside the public highway. We would also urge landowners to consider and carry out tree planting of appropriate species to replace any ash trees that are lost. Alternative species for planting are suggested in the Chalara manual - 2. Managing ash trees and woodland, including logs and firewood.

Ash dieback will continue to be monitored closely in accordance with established highway policy. Hampshire Highways is also committed to replacing any highway tree that is removed for highway safety and where space allows and will consider new sites suitable for tree planting where there is sufficient space above and below ground.

Report a tree problem

Ash trees